Machines such as, for example, cars, trucks, wheel loaders, backhoes, and tractors, include motion-control systems that have one or more moveable input devices that regulate the motion of one or more moveable components, such as ground wheels of a machine. Some such motion-control systems include an operator interface associated with the moveable input device, such as a joystick, steering wheel, or a pedal, that an operator uses to provide input to the motion-control system. In some cases, such an operator input device provides inputs to regulate the motion of the moveable components through a mechanical connection. Such mechanical connections can transmit force feedback from the moveable components to the operator input device. Other motion control systems use means other than a mechanical connection to transmit input from the operator input device to the moveable components of the motion-control system, such as electrical signals (steer-by-wire type steering system). Some of these steer-by-wire steering systems provide force feedback to the operator manipulating the operator input device by, for example, calculating an error between the position of the operator input device and the position of the moveable components and applying a force feedback.
In some situations, certain types of force feedback between the moveable components and the operator input device may be undesirable. For example, the moveable components connected to the operator input device may be ground wheels of a machine. When the ground wheels encounter a significant obstruction or imperfection in the road, the operator may feel a kickback through the operator input device. The force of this kickback can be large and sudden, and a potential hazard for the operator of the machine. Furthermore, the operator tends to over-correct the operator input device in response to such sudden movements of the operator input device, resulting in suboptimal steering. Mechanical steering systems have various means of preventing such kickback. Electrical steering systems that provide force feedback based on error between the position of the operator input device and the position of the moveable components are not equipped with a suitable way to prevent such kickback. However, it might be desirable or necessary to prevent such kickback forces being transmitted to the operator input device in such systems.
An exemplary system that may be utilized to reduce the transmission of kickback to the operator input device in an electrical steering system is disclosed in U.S. Pat. No. 7,516,812 to Hara et al. that issued on Apr. 14, 2009 (the '812 patent). The system of the '812 patent is capable of increasing the steering reaction force in a steering wheel in response to road surface reaction forces on ground wheels when the steering wheel is turning, and decreasing the steering reaction force in response to the road surface force when the steering wheel is returning. The system mitigates changes in the steering force accompanying shocks from transient increases in road surface reaction forces such that the operator can smoothly return back the steering wheel to the center position.
Although the system of '812 patent may be useful for allowing a smooth return of the steering wheel by decreasing the influence of ground-induced forces on the steering reaction force during the period of return for the steering wheel, the system does not remove kickback to the operator input device during all circumstances, while still providing for force feedback to the operator input device when kickback is not occurring.
The disclosed steering system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.